**1. Introduction**

As a teacher in high school education, my intent to find answers to my questions about behavior and learning difficulties my students used to have made me think

about the failure I was experiencing trying to help them. What was missing in my approach? As a biologist, I know that an individual has his genes, the environment can regulate their expression, and the development of each living being has a unique complexity. Then I realized that if I wanted to help my students, I would need to research beyond the answers in the classroom. It was when I began to study more deeply how learning development occurs in humans, including in a comparative aspect, which revealed to me the complexity of the process. Sharing my experiences with a great friend, who also investigated education for a longer time, together with a team, we developed a material in order to experience another way of teaching and learning in the classroom. Working with that material with my students in high school, in some aspects, such as the movements, I observed surprising changes in students that presented learning difficulties because they developed the pleasure to learn and discover. This experience was replicated in public schools in Monteiro Lobato city, in middle school, with equally surprising results. These experiments were carried out in 2007 in high school and in 2011 in middle school and published in an article in 2014 [1].

Continuing with our studies, we decided to investigate more about childhood: how far things I observed in students in high school would be the result of experiences up to 6 years of age? We agreed that I would research the physiological aspects of development. That is when I organized the knowledge about child development in Physiology, under nutrition, cognition, motricity, metabolism, and epigenetics, produced in academic institutions, in order to process all this knowledge into a language easy enough to people not belonging to these institutions could understand it, even those who knew a little about child development. After all, a child's development depends mainly on the environment that adults around him offer him.

### **2. Physiology under an integrated approach of systems and definitions**

A living system is an open, self-organized system in which there is a continuous exchange of matter and energy with the environment so that life persists. A complex interdependent system that floats and oscillates within limits controls the internal state of plasticity and flexibility. In an attempt to understand this complex system, the biological sciences adopted Descartes' metaphor, which places the functioning of the world as a machine. Over time, this metaphor has been replaced as a truth, simplifying a complex question and dividing it into parts that add up when they are interconnected, forming a whole greater than the sum of its parts. Studying a living system under this mechanistic reductionism limits its understanding, for there is no single obvious way to divide an organism into organs that are appropriate for a causal analysis of different functions: The organism is a nexus of a large number of weakly determined forces, none is dominant. The separation of causes and effects becomes problematic because organic processes have a historical contingency that hinders universal and generalist explanations [2]. The actions and events that occur since the emergence of the individual are cumulative and influence throughout life: in the way they self-organize, grow, develop, adapt, reproduce, repair, and maintain form and function, age, and die.

Development, in the context of this work, is considered as an unfolding of something already present and somehow pre-formed: The ontogeny of an organism is the consequence of a singular interaction between the genes that it carries, the temporal sequence of the external environments through which it passes during life *Integration of Motor, Cognitive, Nutritional, Metabolic, and Epigenetic Influence Variables… DOI: http://dx.doi.org/10.5772/intechopen.113145*

and random events of molecular interactions between the cells of the individual [2]. Studies, in both humans and animals, reveal that factors that act in early life influence energy balance in the long term [3]. One way to study this energy balance is by measuring the basal metabolism of individuals.

Basal metabolism is the energy expended by cellular and tissue processes to ensure the maintenance of life [4], which is different in adults and children. Basal metabolism in children is proportional to body mass rather than following the coefficient of 0.75 identified in adults. During childhood, basal metabolism mainly corresponds to the activities of the brain, liver, heart, and kidneys. In the newborn, for example, the contribution of the brain to basal metabolism is about 87%. During the first year of life is approximately 53 to 64%. In the case of chemical processes, such as protein synthesis and ion pumping, it is about 2/3 or more of basal metabolism. Significant changes occur in body mass composition during the first year of life. Therefore, the energy cost of growth varies during childhood [5]. When the proportions related to body mass composition stabilize at the end of early childhood (from 0 to 6 years), the basal metabolism coefficient is 0.75, as identified in adults. Before this point, preparing meals for a child is very different compared to an adult: Nutritional needs are very different and vary enormously during the first year according to the specific patterns of growth of the baby and the amount of motor stimulation. In addition, the baby performs various physiological adjustments, adjusts the immune system, and needs adequate nutrition to survive. The type and consistency of food change as the gastrointestinal system matures, becoming capable of metabolizing components and excreting metabolites from complex foods. The introduction of solid foods should occur parallel to the changes that occur in the development of the central nervous system during the first year, which provides a level of readiness for the baby to cope with foods of various textures, from liquid to soft [6]. In addition, human studies and animal experiments demonstrate the crucial role of nutrition in neuronal development: There is strong evidence that the diet of pregnant women, babies, and children has a long-term influence on cognitive development [7].

Considering as a general principle that the central nervous system is very vulnerable when it is developing rapidly, such a period known as a "growth spurt," nutrition has the greatest effect on brain development during the perinatal period, between the third trimester of pregnancy and the first months of a human baby's life. During this period of rapid growth, neural events occur according to a well-established schedule, so the effects of nutrition depend on when these events happen [8, 9]. Any change in the basic neuronal structure brought about by nutrition seems to have a long-term effect. Humans do not passively respond to environments in which they are: Cognitive processes affect environment choices and cognition is implicated in food choices [9]. Therefore, an adequate balance of energy and essential nutrients are dietary requirements for proper growth and development during childhood.

When cognitive development is disturbed, motor development is often affected. Motor development and cognitive development can be fundamentally interconnected and exhibit equally extended "development schedules" [8]. Motor development in children can be described as a dynamic process in which new forms of movement emerge from intrinsic processes and through interaction with the environment [10]. The assessment of a child's motor development has been considered one of the most important indicators of possible problems in neurological development [11]. Motor behavior involves more than performing muscle activity, joints, and strength. Adjustments in motor behavior to what the body needs about the environment require perception, planning, decision-making, learning, and discovery of new strategies.

Motor development comprises the development of the body, brain, and interaction with the environment [12].

Before moving forward, it is necessary to make a parenthesis to clarify some concepts used here that, sometimes, in many readings, are used as synonyms, such as adaptation and adjustment. According to Schmitd-Nielsen [4], the concept of adaptation refers to behavioral or genetic changes that occur in species over generations, while it adjusts to the changes that occur in the individual, i.e., a single generation adjusts itself to changes in the environment. Therefore, when the word adaptation is being used by authors as a synonym for adjustment, in this work, the term will be corrected into adjustment. The same was observed for the concepts of growth and development. This work follows the definitions given [13]: Growth refers to observable changes in quantity, that is, the increase in body size due to successive cell divisions; processes of change in the level of functioning of the individual as a consequence of their growth. For this reason, the term child development was chosen, not growth, because child development is the specialization of functions over the first 6 years of life.

### **3. Historical perspective of child development studies**

#### **3.1 Preformationism theory**

For centuries, childhood was disregarded: Children were like miniatures of fully formed adults. According to Àries [14], people treated children like adults in the Middle Ages. When they were 6 or 7, children were taken to other villages to work as apprentices, wore the same clothes as adults, and went to taverns with their parents. Children under the age of 7 used to receive protection and care. However, people were indifferent to the stimuli provided to children in this age group, such as motor and speech development [14]. According to Ausubel & Sullivan [15], the fundamental thesis of preformationism denies the importance of development in human ontogeny. All characteristics, whether physical, motor, cognitive, or emotional, are pre-existing and pre-formed at birth.

The change in the preformationist view was gradual and began approximately in the 1500s when the world of work showed signs of change. With the invention of the mechanical press, the growth of trade and economic markets, and the emergence of cities and national states, new job opportunities began to emerge: merchants, lawyers, bankers, journalists, government officials, and occupations that required knowledge of reading, writing, and mathematics. Members of a growing middle class began to discredit that a person's place in society was predetermined by birth. They saw, in children, the possibility of ascending socially, providing their children with the necessary academic education for these new jobs. This new demand for education caused the number of schools in Europe to grow greatly in the sixteenth and seventeenth centuries [16]. The child, then, was no longer seen as a being prepared for the adult's world, but as someone who needed to be separated from this world to receive an education: The child was seen less as an adult and more as a future adult [14] but not as a child yet.

#### **3.2 The importance of the first years of life**

The first to highlight the importance of childhood care was John Locke (1632–1704). In his book "Some Concerns About Education," from 1693, the author points out that "the smallest or hardly felt an impression in our early childhood is paramount and

*Integration of Motor, Cognitive, Nutritional, Metabolic, and Epigenetic Influence Variables… DOI: http://dx.doi.org/10.5772/intechopen.113145*

leaves consequences" [17]; and also highlights the care of the child, which "should be, not what a doctor should do with a sick and agitated child; but what parents, without the help of a doctor, could do to prevent possible diseases and maintain a healthy constitution of their children" [17]. For him, experience is where all knowledge is founded and from where we derive. The environment shapes the mind, and its influence [of the environment] is stronger in the first years of life, a period when one can mold the child for his whole life. According to Locke, many of our thoughts and feelings develop by association, behaviors, by repetition, and we learn by imitation and rewards and punishments. These three factors together would shape character [16, 17].

Although John Locke wrote a philosophy for education and its principles [16] and, in his book, dedicated itself to the physical care he should have with children in the early years, he did not distinguish the stages of child development.

#### **3.3 Child development by stages**

Jean Jacques Rousseau (1712–1778) was the first to describe child development as independent of the influences of the environment and as something that happened according to an internal, biological timeline in the eighteenth century. Children were not shaped only by external forces but also grew and learned a lot by themselves following a plan [16]. Rousseau suggested that development unfolded in a series of stages, periods in which the child experienced the world in different ways. That was the difference between a child and an adult: They were not blank canvases to be filled with the teachings of adults, but the patterns of thought and behavior of each child would have unique characteristics of each stage [16, 18]. For Rousseau [18], each child should be treated according to his stage. He also did not believe in the "power of the environment," especially the social environment, to form a healthy individual. According to Rousseau, instead of teaching the child to think "correctly," we should allow him to perfect his own abilities and learn by his own means, to rely on his own judgment power [16, 18].

A century after Rousseau, the British naturalist Charles Darwin (1809–1882), after his expedition to distant parts of the world aboard the Beagle, wrote the foundations of what would become the Theory of Evolution, with emphasis on the adaptive value of physical characteristics and behavior for the survival of the individual. During his exploration, Darwin discovered that the prenatal growth of many species was surprisingly similar. From this observation of Darwin, other researchers followed the same general plan for the evolution of the human species, carefully observing all aspects of the child's behavior, and conducting scientific studies on child development [19].

Influenced by the Theory of Evolution and studies in genetics, Arnold Gesell (1880–1961) was the pioneer in studies on biological maturation and the first to develop tests for child intelligence [16].

According to Gesell, maturation refers to the processes by which development is governed by intrinsic factors, mainly genes, which are chemicals contained in the nucleus of each cell. Genes determine the sequence, timing, and emergence of action patterns in conjunction with environmental factors. For this author, child development is influenced by two main forces: the environment, which would be the external force, and genes, which would be the internal force. For Gesell, babies come into the world with an internal clock, which is the product of 3 million years of biological evolution. Therefore, they are preeminently "wise" about their needs and what they are or are not ready to do. Gesell emphasized that the first year of life is the best time to learn about the child's individuality and that parents, despite an intuitive sensitivity to the child, needed some theoretical knowledge about child development [16, 20].

#### **3.4 Sensitive periods (windows of opportunity)**

In 1891, the term "sensitive periods" was first used by botanist Hugo De Vries (1848–1935) when describing a specific period when poppy flowers were sensitive to the external environment to the point of causing the modification of stamen (male structure of a flower) in the secondary pistil (female structure of a flower). According to De Vries, this sensitive period comprised the seed phase or the first weeks of life of the young plant [21]. Contemporary of De Vries, Maria Montessori (1870–1952), in her book "Il Secreto dell'Infanzia"1936, cites De Vries as the author of the term and uses it to determine the periods that are genetically programmed in time blocks during which the child is especially able to learn certain tasks very well. For example, there are periods for the development of language and the beginning of the use of hands [22]. The concept of "sensitive periods" is a central component of child development for Montessori [16]. According to the author, if the child is prevented from enjoying the experiences at the time when nature planned for him, the "special sensitivity that draws" will disappear, having a disturbing effect on development [23].

Studies conducted on fish embryos in the early twentieth century showed that there were critical periods when interference with the embryonic development of these animals, such as food deprivation, would have "more serious results" than in any other period [24]. Stockard [24] does not explain the term "critical period" *per se*, but is the first to use it in a scientific work to explain periods in the development of a species in which interventions would be more or less determinant in the development of the individual and that the processes of maturation in different parts would happen at different rates. This concept was adopted by neurobiology, whose research revealed that different regions of the nervous system of children matured in different periods [25]. The effect of a given stimulus (or experience) on development depends on when it occurs during that development, and in most cases, there is a window of opportunity in which a particular stimulus can influence it. If a certain stimulus must happen at a particular interval of development, this interval is called a "critical period." However, when a particular stimulus needs to occur at a certain interval, but still influences, even if more leniently, outside that interval, that larger interval is called the "sensitive period." Although the term "critical period" is more used, most of the effects of stimuli occur in sensitive periods [26].

The concept behind this term is that certain windows are opened to the effect of external experiences, from birth, closing one by one, with increasing age, because of the decline of the plasticity of the brain. There are windows to the development of motor control, vision, feelings, and language. In theory, if the child loses an opportunity, he can no longer develop the neuronal circuit with all its potential for a specific function [13], as described by Montessori. This is because if a neuronal circuit, once formed, is not used, it can be lost and not work properly—it is the principle of "use it or lose it." One of the advantages of human brain development taking a long time is that many stimulation opportunities and experiences can be promoted to enable fine-tuning of development [26].

#### **3.5 Epigenetics and critical periods**

According to the Origin of Development hypothesis, during critical developmental periods (prenatal and postnatal mammals), nutrition and other

#### *Integration of Motor, Cognitive, Nutritional, Metabolic, and Epigenetic Influence Variables… DOI: http://dx.doi.org/10.5772/intechopen.113145*

environmental stimuli influence the pathways through which development will follow. Numerous studies show an association between low birth weight and the incidence of cardiovascular disease, hypertension, type 2 diabetes, and deficiencies in insulin metabolism and serum cholesterol concentrations in adults. From the point of view of epigenetics (the study of heritable traits that are not associated with changes in the sequence of nucleotides – which form genes, the basic physical and functional unit of heredity – but with chemical changes in DNA, which is made up by genes, or regulatory and structural proteins that are linked to it [27, 28]), child development could be defined as "carved experiences into DNA of an organism through one of the main epigenetic mechanisms of change: methylation." DNA methylation corresponds to the chemical transfer of a methyl group to a CpG sequence (cytosine-phosphate-guanine) in one of the DNA strands. This mechanism is generally related to gene silencing, whether of paternal or maternal origin, during embryogenesis, as well as after birth [29–31]. The DNA methylation machinery sets the standards during development and possibly during adulthood in response to new signals from the environment, which are renewed when the genome is duplicated in mitosis [32–36]. Therefore, child development could be defined as a dynamic interaction between the environment and the child and mediated by a series of epigenetic modifications of specific genes that would result in physiological, stable, and persistent cognitive, emotional, and behavioral. Fraga and collaborators [37], studying monozygotic twins, discovered substantial epigenetic differences between them. According to van Ijzendoorn and collaborators [30], this was possible because identical twins were exposed to different environments and, because of this, would no longer be identical. Many studies suggest that childhood trauma may induce depression, anxiety, and posttraumatic stress response by epigenetic regulation of the hypothalamic-pituitaryadrenal axis, which is responsible for stress response [38]. Epigenetic changes would be the molecular mechanism by which the environment would affect the physiology and behavior of a developing child, and development would incorporate environmentally induced signatures into the epigenome [30, 37], whose modifications could be transmitted throughout generations. Heijmans and collaborators [39], studying individuals who were exposed to famine during Dutch Hunger Winter in 1944–1945, showed that those individuals, 6 decades later, had less DNA methylation of the imprinted gene IGF-2 (related to insulin response to glucose so to overweight, obesity, and type 2 diabetes [40]), compared to their same-sex unexposed siblings. Early-life environmental conditions can contribute to epigenetic modifications that affect the individuals throughout their life and their next generation.

### **4. The importance of an integrative approach of child development**

Considering development as an unfolding of something already present and somehow preformed, the ontogeny of an organism is the consequence of a singular interaction between the genes it carries, the temporal sequence of the external environments through which it passes during life, and random events of molecular interactions between the cells of the individual [2]. Studies, both in humans and in other animals, reveal that factors that act in early life influence the long-term energy balance [3]. Nutritional physiology often undergoes programmed changes throughout development as individuals mature from birth to adulthood [41]. Considering human beings, movements depend on biological and psychological environments as on conditions of the environment where they live and are built throughout their lives [42], which is no different for any other animal. Therefore, the first years of life are essential for the foundation of later development: The young and the adult are the result of the quality of care they had in childhood.

Child development includes interdependent dimensions that encompass social, emotional, cognitive, psychomotor and patterns of behavior, and nutrition [43]. According to Fonseca [44], for Piaget, all cognitive mechanisms are based on and emerge from the development of motor skills, which occurs in early childhood (from 0 to 6 years of age). Fonseca [44] states that psychomotricity helps the child to acquire sensations, perceptions, and concepts that will allow him to know his own body and, from it, the world around him. Ivanovic and collaborators [45] found that the differences in IQ among Chilean high school students were mainly due to malnutrition in childhood. According to Cadavid Castro [46], it is increasingly clear that the quantity and quality of nutrients received by the child are directly related to their cognitive potential and their mental and emotional health, in addition to reflecting on adult brain functions and their eventual decline with age. Childhood is the crucial phase in which many health-related behaviors are shaped [47], and a child does not choose the environment in which he lives, much less has the skill and knowledge necessary to choose a diet or exercise. According to the World Health Organization, only 3% of cases of type 2 diabetes and obesity were observed in children in the United States in the mid-1970s [43]. Currently, this proportion reaches 45% of cases, with alarming rates in other countries, including Brazil. Children depend on their parents to have a healthy childhood: Parents who know which nutritional and psychomotor factors are important to a child can educate them to be active, with full development of their cognitive and motor abilities. In the future, this child will be able to choose his own path, such as dedicating himself to sports or "books," for example, and not simply exclude one for not feeling able to perform the other [48].

The passage from a limited motor repertoire of the newborn to complex motor skills and manipulation of the child is among the most dramatic and visible transformations in the human life cycle. Because of this, many researchers believed that these transitions could promote a model of understanding the development of higher cognitive functions or even be underlying higher functions [49].

However, the scenario for the promotion of child development around the world is far from the best: At least 200 million children under the age of five cannot develop their cognitive and socio-emotional potential, basically because of nutritional deficiencies, malnutrition, and inadequate stimuli in the first years of life. Each of these related factors leads to a determining effect on the development of the child. But when two or more of these factors are found together, the combined impact of the factors is even more severe [50]. Understanding how all these factors are interrelated (cognition, motricity, nutrition, metabolism, and factors of epigenetic influence) can contribute to the further understanding of the complexity of human development, which is far beyond studying each phase or each aspect separately, but first of all in knowing how each factor interacts with each other throughout life [51–54]. We have a big problem ahead of us. The kind of problem is defined and, along with it, the seriousness of its long-term consequences. A response is needed from the world and from us [50].
